1. Field of the Invention
The present invention relates to a serial recording apparatus equipped with a carrier for causing a recording head to execute a scanning motion relative to a recording medium, and more particularly to the driving of the carrier in the recording apparatus capable of recording both in the forward and reverse directions.
2. Related Background Art
Among serial printers for executing recording operation by driving a recording head mounted on a carrier while moving the carrier along a recording sheet, there is already known a serial printer capable of recording both in the forward and reverse motions of the carrier in order to increase the recording speed.
As a representative example of such serial printer, there is widely known an ink jet serial printer effecting the recording operation by discharging ink from a recording head onto a recording sheet.
FIG. 2 is a schematic view showing the configuration of a serial printer of the ink jet method. A carrier 1 is supported by a guide shaft 2 and a guide rail 4 so as to be capable of reciprocating motion relative to an LF (line feed) roller 5 and a platen 6 supported by a chassis 3. A recording head 7 is mounted on the carrier 1, and executes reciprocating motion along the guide shaft 2, by the power of a carrier motor 8 transmitted by a belt 9.
A recording sheet 10 is supported in the printer by being held between the LF roller 5 and a pinch roller 11, and is transported perpendicularly to the axis of the LF roller 5 by the frictional force by the rotation of the LF roller 5.
In the recording operation, the carrier motor 8 is driven with an acceleration table of a predetermined number of steps to shift the carrier 1 from the stopped state to an acceleration state. Thereafter the carrier motor 8 is driven with a predetermined driving frequency, whereby the carrier 1 moves at a constant speed. In this state the recording head 7 is driven according to recording data transferred to the printer, thereby discharging ink toward the recording sheet 10. After the driving of the recording head 7 for a line, the carrier motor 8 is driven with a deceleration table of a predetermined number of steps to decelerate the carrier 1, eventually bringing it to a stopped state.
Also after the recording of a line, the LF roller 5 is rotated by a predetermined amount to transport the recording sheet 10 in such a manner that a portion thereof to be recorded next is brought to a position opposed to the recording head 7. After this operation, the carrier motor 8 is driven again to move the carrier 1 and the recording head 7 is driven again during the motion of the carrier 1 to record the next line. When all the recording data are recorded by the repetition of the above-described operations, the recording sheet 10 is discharged by a discharge roller 12 to the exterior of the printer, whereupon the recording operation is completed.
In the printer of the above-described configuration, if the recording operation is executed only in one moving direction in the motion of the carrier 1, there is required a returning operation for returning the carrier to the start position after the recording of each line, thus resulting in a significant loss in increasing the recording speed.
For this reason, high-speed recording is generally achieved by eliminating such loss in time, by so-called two-directional recording in which the recording is executed both in the forward and reverse motion of the carrier 1.
FIGS. 3A and 3B show the concept of carrier drive in the conventional two-directional recording. In the recording operation while the carrier 1 is driven in a direction from right to left in FIG. 2 (hereinafter called forward direction), the carrier motor 8 is driven with an acceleration table AC1 and a deceleration table DC1 as shown in FIG. 3A, whereby the carrier is moved in the forward direction. In case of carrier movement in a direction from left to right (hereinafter called reverse direction), the carrier motor 8 is driven with an acceleration table AC2 and a deceleration table DC2 as shown in FIG. 3B, whereby the carrier is moved in the reverse direction.
As the frictional force generated between the carrier 1 and the guide shaft 2 or the guide rail 4 functions as a braking force, the deceleration is generally achieved with a fewer number of steps or with a shorter moving distance than in the acceleration. Therefore, the number NAC1 of driving steps for the carrier motor 8 at the acceleration and the number NDC1 of driving steps at the deceleration satisfy a relationship NAC1&gt;NDC1. Similarly at the recording operation in the reverse direction, there stands a relationship NAC2&gt;NDC2 between the number NAC2 of driving steps for the carrier motor 8 at the acceleration and the number NDC2 of driving steps at the deceleration. In FIGS. 3A and 3B, SC1 and SC2 indicate printing ranges.
However, in the two-directional recording, in order to record in a same recording range both in the forward recording and in the reverse recording, it is necessary to employ a same number of driving steps for the acceleration and for the deceleration, thereby realizing a same moving distance of the carrier in the acceleration and in the deceleration.
For this reason, in the recording in the forward direction, the deceleration is started after a movement by a predetermined distance .DELTA.S, whereby the movement amount SAC1 of the carrier 1 in the acceleration is made equal to the movement amount SDC1' of the carrier 1 from the end of recording to the stopping of the carrier 1. Similarly, in the recording in the reverse direction, the deceleration is started after a movement by a predetermined distance .DELTA.S, whereby the movement amount SAC2 of the carrier 1 in the acceleration is made equal to the movement amount SDC2' of the carrier 1 from the end of recording to the stopping of the carrier 1. The distance AS is defined by .DELTA.S=SAC1-SDC1=SAC2-SDC2.
Therefore, for a given movable range S1 of the carrier 1, the recordable range becomes narrower by .DELTA.S in comparison with the one-directional recording.
In summary, in the conventional serial printer capable of two-directional recording, the recording range is defined by the mutually overlapping area of the recordable range in the forward direction and that in the reverse direction, and the moving range of the carrier has to be made wider in order to expand the recordable range. Consequently, the width of the printer has to be made considerably larger than the minimum necessary width of the printer required for the recordable range, and such configuration is disadvantageous in dimension and cost of the printer.
As explained in the foregoing, in the conventional serial printer capable of two-directional recording, the moving distance of the carrier 1 from the end of recording to the stopping of the carrier 1 is selected equal to the moving distance at the acceleration, and thus larger than the minimum necessary moving distance, so that the width of the printer becomes large in relation to the recording range.